I installed High Sierra and now my iMac (27" 2011) can not see the external USB TimeMachine drive.
The drive shows up in DiskUtil but it's greyed out. I can not mount it. In fact it doesn't respond to any commands, mount, eject, first aid won't run.
I also have a MacBook Pro (High Sierra too), it can't read the drive, same problem.
I tried booting into Recovery mode, I still can't access the drive.
The drive is fine, I can plug it into a Linux machine and I can browse the disc.
How can I fix this?